1. Field of the Invention
The present invention relates to an image forming device, particularly to an image forming device using an electrophotography system which is applied to a copier, a laser printer, a facsimile and the like and in which a two components developing agent comprising a toner and a carrier is used.
2. Description of the Related Art
An image forming device for carrying out image formation by using an electrophotography system is installed with devices which are liable to undergo influence of environmental change and ageing change such as a photosensitive body, a charging device, an exposing device, a developing device and so on. Therefore, an image forming state produced by the image forming device using the electrophotocopy system is varied by temperature, humidity, total number of image formations and the like, so that it is difficult to stably obtain a uniform image forming state.
Hence, according to conventional image forming devices, various image stabilization functions are provided to achieve stabilization of image by controlling process conditions of a charge amount, an exposure amount, developing bias, a toner concentration and so on. For example, in Japanese Patent Unexamined Publication No. JP-A-4-50880, there is disclosed a constitution in which in an image forming device for carrying out image formation by using a two components developing agent, humidity detecting means for detecting an environmental humidity and operating time detecting means for detecting operating time of at developing agent are installed, and when the environmental humidity is increased or the operating time of the developing agent is prolonged, lowering of a charge amount of a toner caused by an increase in the environmental humidity or prolongation of the operating time of the developing agent is prevented by lowering the concentration of the toner in a developing device.
Further, in Japanese Patent Unexamined Publication No. JP-A-4-110977, there are disclosed a constitution in which in order to prevent deterioration in image quality that is caused when a toner is liable to scatter owing to forced replenishment of the toner carried out under a copying forbidden state, the rotational speed of a replenishing roller in case of the forced replenishment of the toner under the copying forbidden state is retarded compared with the rotational speed of the replenishing roller in case of supplying the toner normally, and a constitution in which an interval between the replenishing roller and a scrape member in case of replenishing the toner under the copying forbidden state is made wider than the interval between the replenishing roller and the scrape member in case of replenishing the toner normally.
Furthermore, in Japanese Patent Unexamined Publication No. JP-A-4-213472, there is disclosed a constitution in which when a control value of the concentration of a toner is varied, developing bias voltage and an amount of exposure are changed such that a concentration of an original and a concentration of an image correspond to each other, thereby promoting response performance between control of the toner concentration and control of the image concentration and providing an image having excellent reproducibility and causing no stain in respect of all of the concentrations.
However, although in the image forming device using the two components developing agent the excellency or nonexcellency of the image forming state is influenced also by fluidity, charging performance and the like of a toner in a developing tank, there has been no conventional image forming device in which changes in the fluidity, the charging performance and the like of the toner are detected and appropriate image forming process conditions are controlled. Therefore, there have been cases where image formation is carried out under a state in which inappropriate process conditions are set, and there has been a problem of deteriorating the image forming state.